You are reviewing the Velocity Chart for your team and notice that they completed more...

The reason why your team completed more story points than they committed in their last sprint is that someone increased the story point value on an issue mid-sprint. This will increase the total story points completed at the end of the sprint, but not affect the total story points committed at the start of the sprint. Therefore, it will result in a positive scope change. The other reasons mentioned in the question do not explain why your team completed more story points than they committed, as they either do not affect story points at all, or affect both committed and completed story points equally. References: Viewing the Velocity Chart, Scope change